1. Field of the Invention
The present invention relates to an implantable medical electrode device and, in particular, a cardiovascular cardiac pacemaker or defibrillator electrode device.
2. Description of the Related Art
On the background of the present invention, it is to be noted that implantable electrode devices of this type must be anchored at a specific body location, so that they do not change their position over the course of time. This is especially important when such electrode devices are implanted in a moving organ, such as the heart.
To fix the electrode device, implementing fixing units, such as screws, needles, hooks, anchors (tines), or projections and corresponding undercuts, into which the tissue may grow, on their elongate, tubular electrode bodies in a fixing zone before the distal end is known.
Fixing in a blood vessel represents a special case, since sharp tips or edges of the fixing units may cause injuries or at least irritations on the vessel wall here in particular. For this reason, typical fixing units are designed in such a way that they jam in the vessel because of their shaping.
In addition to the anchoring of such electrode devices, which is as atraumatic as possible, fixing in vessels of various diameters also plays a role.
Electrode devices implantable in vessels, which have the above-mentioned “tines”, silicone screws, or helical and/or hooked electrode bodies, are commercially available. Through pre-shaped electrode bodies of this type, for example, having bending points applied in a targeted way, the electrode body may be applied in a formfitting way to the angles and discharges of veins in the cardiovascular system, for example, and thus achieve fixing. In linear veins, positional fixing may be performed by stretching these targeted bends. Furthermore, electrodes which have an electrode body shaped as a helix on the distal end, which clamps on the vascular wall by expansion forces, are known.
An especially simple fixing technology, which does not achieve optimal therapeutic results, however, is wedging the distal tip of the electrode body in the vessel. The electrode body is advanced into the left-ventricular vein branch, for example, until the tip of the electrode body jams in the vein and assumes a “wedge position”. The vein is closed in this position.
All of the preceding anchoring technologies have various disadvantages, such as the dependence of the final position of the electrode body on the ratio the diameter of the vein to the dimensions of the tip, helix anchors, or “tines”. The final position of the electrode body thus achievable is not necessarily the most favorable therapeutic position.
Reference is made to, for example, WO 98/42403 A1 or U.S. Pat. No. 5,170,802 A of the published prior art. These publications disclose a fixing unit having a “stent”, which is expanded when the electrode device is located at the desired position in the vessel. The electrode body is wedged in position by the expansion of the stent structure. This solution has the disadvantage that the fixing is not reversible, which make detaching and replacing the electrode device after a first fixing, which is sometimes necessary, and also removal of the electrode device difficult.
A solution for the problem of repositioning is disclosed in WO 94/07564 A1, in which the fixing is performed by an expandable or self-expanding wire basket. This construction has the disadvantage that the wires cut into the vascular wall and thus may be very traumatic.
Finally, U.S. Pat. No. 5,411,546 A1 discloses various solutions for fixing in a vessel, for example, wire spirals which are reversibly extendable from the catheter envelope and retractable back therein. However, the fixing is not very reliable, due to the smaller diameter of the wires and the small contact area between spirals and vascular wall connected thereto, and the limited clamping force with which the spirals may press against the vascular wall, so that the latter is not damaged. The wire constructions also disclosed in the publication are—as already mentioned above—highly traumatic. Furthermore, a “sail construction” is also disclosed in this published prior art, which is again not reversible.